JPH01311565A - Electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a high-capacity graphite electrode by using a mixture of high-crystallization graphite and low-crystallization graphite with the spacing of the graphite structure in specific ranges respectively for an electrode active material. CONSTITUTION:A mixture of high-crystallization with the spacing of the graphite structure in the range of 0.3354 to 0.3400nm and low-crystallization with the spacing in the range of 0.343 to 0.355nm is used for an electrode active material. For the manufacture of graphite with different spacings, a hydrocarbon compound which is a starting material is heat-decomposed on a substrate made of iron group elements (iron, cobalt, nickel) or alloys containing them by the chemical vapor phase accumulation method, graphite is accumulated under the preset conditions using the hydrocarbon compound with the molecular weight of 150 or below. Graphite can be efficiently formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an electrode and a method for manufacturing the same, and particularly to an electrode active material for a battery using an alkali metal such as lithium or potassium as a dopant material.

(b) Conventional technology Conventionally, as an electrode for a secondary battery using an alkali metal as a dopant, the interplanar spacing +cb ranges from 0.337 nm to 0.35 nm.
Electrodes using graphite as an active material having a single crystallinity within the range of 5 nm are known (Japanese Patent Laid-Open No. 61-513 and Japanese Patent Laid-open No. 61-1072).

Here, graphite has a structure formed by the spread and overlapping of network planes of six-membered carbon rings, and especially when these six-membered ring network planes overlap very regularly, the interplanar spacing becomes 0.3354 nm, On the other hand, when they overlap more irregularly than this, the interplanar spacing gradually increases as the irregularity increases. The above-mentioned conventional graphite for electrodes had interplanar spacings distributed within the narrow range mentioned above.

(c) Problems to be solved by the invention However, such conventional electrodes using graphite as an active material, which has a single crystallinity and whose interplanar spacing is distributed in a narrow range, have a small electrochemical charge/discharge capacity. There was a problem. In particular, the charge/discharge capacity in the low potential region is small, which is important when operating as a battery in combination with a suitable positive electrode. 18h+A per graphite 1110
It was small, less than h.

The present invention was made to solve the above-mentioned problems, and particularly aims to provide an electrode with a large charge/discharge capacity.

(d) Means for Solving the Problems The present inventors have conducted intensive studies to increase the capacity of such graphite electrodes, and have found that a mixture of specific graphites with different crystallinity based on the interplanar spacing has good electrode properties. We found that this shows that That is, the surface spacing (cb is 0.3354r+m ~ 0.3
Highly crystalline graphite within the range of 400rv and (with a peak of 0.
The inventors have discovered that a mixture with low crystalline graphite in the range of 343ni to 0,355rv is superior to conventional ones in charge/discharge capacity per unit weight in a low potential portion, and has thus arrived at the present invention.

Thus, according to the present invention, the lattice spacing (
d) is within the range of 0.3354ni to 0.3400nm, and the same plane spacing (d+ is 0.343na+
An electrode is provided which uses as an electrode active material a mixture with graphite within the range of 0.355 rv from 0.355 rv.

In this invention, each of the above-mentioned interplanar spacings is usually measured by X-ray diffraction analysis, and specifically,
Determined based on the θ value. Here, the surface spacing is 0.335
Being within the range of 4 to 0.3400 nm does not necessarily mean that the interplanar spacing is distributed over this entire range, but it is sufficient that the interplanar spacing is at least within this range. The same holds true for the range of one surface r1 distance from 0.343 to 0.355no+.

That is, within the range belonging to high crystallinity (0.3354 to 0.3
400ni) and within the range belonging to low crystallinity (0,34ni)
For example, both of these ranges may be continuously distributed on the X-ray diffraction peak.

Among these graphites, in measurements using an X-ray diffractometer using CuKα radiation as a radiation source, the graphite with the smaller interplanar spacing (
002) 2 for the diffraction line intensity of the diffraction maximum peak of reflection
The ratio of diffraction intensity at θ (diffraction angle) -25,0' is 0.03
to 0.90, preferably within the range of 0.03 to 0.50, for example, the charge/discharge capacity at a low potential from Ov to +0.5V with respect to the potential of lithium metal is higher than that of a conventional graphite electrode. It is preferable that it increases by about 1.4 to 1.7 times. When this ratio exceeds 0.9, the ratio of low-crystalline graphite species increases, and although the charge-discharge capacity including the high potential portion increases, the flatness of the charge-discharge curve is lost, and this ratio increases. If it is less than 0.03, the ratio of highly crystalline graphite species will increase, and conversely, although the flatness of the charge-discharge curve will improve, the charge-discharge capacity including the high potential portion will decrease, so in either case This is also undesirable in that the charge/discharge capacity at the low potential portion decreases. Note that the diffraction intensity at 2θ・(diffraction angle) -25,0° is used here instead of the diffraction maximum peak intensity of (002) reflection of the graphite species with a large interplanar spacing. This takes into account the case where the reflection diffraction lines are close to each other and it is difficult to separate both peaks.

In the case of graphite, it is known that the interplanar spacing is a good indicator of crystallinity, and in fact, the half-width of a diffraction peak in X-ray diffraction becomes narrower as the interplanar spacing becomes smaller.

Therefore, the level of crystallinity of graphite can be sufficiently judged by the size of the interplanar spacing as described above.

There are various methods for preparing graphite having different interplanar spacings in the present invention.

In particular, iron group elements (iron, cobalt, nickel) or
On a substrate made of an alloy containing the same, a hydrocarbon compound as a starting material is synthesized by thermally decomposing it by chemical vapor deposition, using a hydrocarbon compound with a molecular weight of 150 or less, and under the following conditions:・Feed rate 0.05 mol/hour ~ 15 mol/hour・
Molecular number density: 2 x 10" molecules/Q - 2,6 x 10" molecules/ρ, flow rate: 0.53/min - 10 molecules/min, thermal decomposition temperature: 450°C - 1300°C (preferably 700°C - 120°C)
By depositing graphite at a temperature of 0° C., the graphite can be efficiently formed. Note that under conditions deviating from these, it is difficult to form graphite having the above-described interplanar spacing, especially graphite with a good balance between high crystallinity and low crystallinity.

The hydrocarbon compound to be removed may be any of aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, etc. Specific examples include benzene, toluene, xylene, naphthalene, etc. , anthracene, hexamethylbenzene, 1,2-dibromoethylene, 2-
Examples include butyne, propane, acetylene, biphenyl, diphenylacetylene and substituted derivatives thereof. Further, a suitable deposition thickness is about 1 to 300 Å.

A substrate made of an iron group element or an alloy containing it used in such a thermal decomposition method can be used as a current collector for a graphite electrode because of its conductivity. Therefore, according to this method, the synthesis of the graphite active material made of the graphite and the formation of the graphite electrode can be performed simultaneously, and it is also preferable for practical use. Note that the substrate in this case is not limited to a flat plate shape, and may be in any form such as a foamed shape or a net shape.

However, the graphite of the present invention can also be produced by, for example, pulverizing and mixing low-crystalline graphite such as pitch-based carbon and high-crystalline graphite such as carbon fiber subjected to high-temperature heat treatment, and firing the mixture.

The electrode thus obtained can be used as an electrode for various batteries, and particularly can be suitably used as a negative electrode for a secondary battery using an alkali metal as a dopant.

(e) Since high-crystalline graphite and low-crystalline graphite, which are characterized by different working surface spacings, coexist, the charge/discharge capacity at the low potential part of the graphite electrode is different from that of the conventional single crystalline graphite. This increases significantly (for example, about 1.4 to 1.7 times) compared to that made of graphite. The charge/discharge capacity at this low potential portion is useful for improving battery performance such as battery capacity per battery life when the graphite electrode is combined with a suitable positive electrode and operated as a battery.

On the other hand, the above-mentioned electrode can be manufactured in a controlled manner by a method of synthesizing graphite by thermally decomposing a hydrocarbon compound as a starting material on a substrate made of an iron group element or an alloy containing it. Can be manufactured well.

(F) Examples Example 1 A nickel base material is placed in a CVD apparatus, and benzene is supplied and thermally decomposed using a chemical vapor deposition method.
Graphite was grown on the base material (90/J) to form a graphite electrode. The reaction conditions for the chemical vapor deposition method at this time were a supply rate of 1.5 mol/hour and a molecular number density of 1.5 mol/hour. OX10
"Molecular/ρ, flow rate 1.5C11/min, thermal decomposition temperature 950
It is ℃.

According to the X-ray diffraction pattern using CuKa rays as a radiation source, the graphite synthesized in this way has a 2θ-26
, 3° (corresponding to a lattice spacing of 0,339 nm) (00
2) It is a mixture of highly crystalline graphite that has a reflection peak and low crystalline graphite that has a peak at 2θ = 25° (corresponding to a lattice spacing of 0.356 rv) on the lower angle side; The ratio of the diffraction intensity of the low crystalline graphite to that of graphite was 0.18.

Next, this graphite electrode is placed in an electrolytic cell, lithium metal is used as a counter electrode, lithium is used as a dopant material, and 1
Using propylene carbonate in which mol/ρ of lithium perchlorate was dissolved and lithium as a reference electrode, a charge/discharge test was conducted by doping and dedoping with lithium atoms. As a result, the potential change during discharge with respect to the lithium reference electrode is shown by curve A in FIG. 2, and the battery capacity was significantly improved in the low potential region of about 1 V or less compared to the comparative example described later.

Example 2 In Example 1, using propane instead of benzene,
Feed rate 2.2 mol/hour, molecular number density 1.5x
Graphite was synthesized in the same manner as in Example 1, except that the flow rate was 0.7 cm/min, and the thermal decomposition temperature was 900°C.

The synthesized graphite is a mixture of highly crystalline graphite and low crystalline graphite, according to the X-ray diffraction pattern shown in Figure 3 using Cu Ka rays as a radiation source, and the 2θ ratio for 2θ = 26.3°
The ratio of diffraction intensities at −25 and 0 degrees was 0.23.

Next, this was used as a graphite electrode in the same manner as in Example 1, and a charge/discharge test was conducted. The results are shown in track 1iAB of FIG. 2, and the capacitance in the low potential region was significantly large.

Comparative Example In the X-ray diffraction pattern using CuKa radiation as the radiation source,
2θ-26,3″ (plane spacing 0.33″) as shown in Figure 4.
A charge/discharge test by doping and dedoping with lithium atoms was conducted in the same manner as in Example 1 using a graphite electrode made only of highly crystalline graphite (equivalent to 9 nm). Curve C for this second concentration factor was obtained, and the capacitance in the low potential region was small.

(G) Effects of the Invention The electrode of the present invention has increased charging and discharging capacity in the low potential portion compared to ordinary crystalline single graphite.

Therefore, when the electrode of the present invention is combined with a suitable positive electrode and operated, for example, as a battery, it is useful for improving the performance of electricity and oil. And since it is easy to manufacture,
Its usefulness is extremely great.

[Brief Description of the Drawings] Figures 1 and 3 are graphs showing the main parts of the X-ray diffraction chart of graphite synthesized in Examples of the present invention, and Figure 2 is a graph showing the main part of the X-ray diffraction chart of graphite synthesized in Examples of the present invention. FIG. 4 is a graph illustrating the main part of an X-ray diffraction chart of a conventional graphite electrode. 71 Figure 2r21 tit/mAhg-' Figure 3 Figure 4 2Q/7i

Claims (2)

[Claims] (1) Plane spacing (d) in graphite structure is 0.3354n
An electrode using, as an electrode active material, a mixture of graphite having a surface spacing (d) within a range of 0.3400 nm from 0.3400 nm and graphite having a surface spacing (d) within a range of 0.343 nm to 0.355 nm. (2) The electrode according to claim (1), wherein graphite is formed by thermal decomposition using a chemical vapor deposition method using a hydrocarbon compound as a starting material on a substrate made of an iron group element or an alloy containing the same. A method for manufacturing an electrode, comprising: manufacturing an electrode.